1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method, in which a substrate to be polished such as a silicon substrate is polished by CMP (Chemical Mechanical Polishing).
2. Background Art
A semiconductor substrate such as a silicon substrate (hereinafter referred to as a substrate) with buried interconnections and interlayer insulating films formed has protruded portions and recessed portions on a surface of the substrate. Recently, as patterns have been miniaturized, when process steps are proceeded with protruded portions and recessed portions existing on the substrate surface, pattern disconnection of upper interconnections and defocus at a step of exposure for forming a resist pattern result from steps or level differences, significantly reducing production yield. In order to prevent such problems, conventionally, the polishing method referred to as CMP has been used, in order to planarize the substrate surface.
This method will be described with reference to FIGS. 6A, 6B and 6C. These figures represent positional relation between a polishing pad and the substrate when the substrate is polished by the conventional polishing apparatus and polishing method, time sequentially, for each unit time. In FIGS. 6A, 6B and 6C, a polishing pad 100 fixed on a surface plate (not shown) rotates about a surface plate axis A. To an upper surface of polishing pad 100, liquid (not shown) referred to as slurry containing abrasive grains such as silica is supplied. A substrate 101 held by suction, for example, is pressed against polishing pad 100 while it is rotated about a substrate axis B, whereby an object of polishing on the substrate surface is polished.
In the CMP, a chemical reaction attained by chemicals such as KOH solution and mechanical polishing attained by the abrasive grains, both of which are contained in the slurry, are utilized to planarize the substrate surface. Here, generally, the number of rotation of the polishing pad 100 is set to be higher than the number of rotation of substrate 101.
In the conventional polishing, however, it is difficult to increase polishing rate for planarization, that is, to increase thickness of the object of polishing removed per unit time. In the following, description will be given taking a small area Q on the surface of substrate 101 shown in FIGS. 6A, 6B and 6C as an example.
The polishing rate depends on the characteristics of the chemicals and the abrasive grains with respect to the material of the film formed on the surface of substrate 101, and on the area at which the small area Q and polishing pad 100 are in contact with each other per unit time (hereinafter referred to as xe2x80x9ccontact areaxe2x80x9d). Accordingly, when the numbers of rotation of polishing pad 100 and substrate 101 are increased, contact area increases, and therefore, the polishing rate increases.
Now, consider a specific abrasive grain of polishing pad 100. The direction at which the abrasive grain contacts with the direction of rotation of substrate 101 is limited. For example, an abrasive grain existing on a virtual arc 102 close to an outer periphery of polishing pad 100 moves in the 5:00 direction (direction of arrow S with respect to arrow R), 6:00 direction and 7:00 direction (direction of arrow U with respect to arrow T) relative to the direction of rotation of substrate 101, and is brought into contact from these directions. Generally, an abrasive grain extending on a virtual arc 103 in the middle between the outer periphery and the center of polishing pad 100 moves in the 4:00 direction (direction of arrow W with respect to arrow V, 6:00 direction and 8:00 direction and is brought into contact from these directions. Similarly, an abrasive grain existing on a virtual arc 104 close to the center of polishing pad 100 moves in the 2:00 direction (direction of arrow Y with respect to arrow X), 12:00 direction and 10:00 direction and is brought into contact from these directions.
In this manner, each abrasive grain is brought into contact only from a specific range of directions with respect to the direction of rotation of substrate 100. In other words, each of the abrasive grains existing on virtual arcs 102, 103 and 104 on polishing pad 100 is brought into contact with each small area of substrate 101 from a prescribed range of directions. This means that individual abrasive grain tends to wear in a biased manner (uneven wear), and therefore, even when the numbers of rotation of polishing pad 100 and substrate 101 are increased, increase in the polishing rate stops after a while.
Further, from the position of FIG. 6A to the position of FIG. 6C, the small area Q only moderately moves, drawing a simple arc with the substrate axis B being the center, with respect to polishing pad 100. In other words, on polishing pad 100, each small area of substrate 101 moves moderately, drawing an arcuate orbit. Therefore, when fragments of abrasive grains dropping out from the upper surface of polishing pad 100 or fragments removed from the surface of substrate 100 cause a clogging, it is difficult to remove the clogging, as each small area of substrate 101 moves arcuately. This makes it difficult to increase the polishing rate.
The present invention was made to solve the above described problems, and its object is to provide a polishing apparatus and polishing method that can increase the polishing rate.
In order to solve the above described technical problems, the present invention provides a polishing apparatus in which a substrate to be polished rotated by a substrate shaft is pressed against a polishing pad with a prescribed pressure, while slurry is supplied to an upper surface of the polishing pad rotated by a surface plate shaft, so that the surface of the target substrate is polished, including a rotating mechanism that rotates at least one of a surface plate axis as a rotation central axis of the surface plate shaft and a substrate axis as a rotation central axis of the substrate rotating shaft about a corresponding prescribed eccentric axis.
Accordingly, on the polishing pad, distance of movement of a small area held by the substrate to be polished increases and, hence, contact area between the small area and the polishing pad increases.
Further, each abrasive grain held by the polishing pad comes to be brought into contact with a small area of the substrate to be polished, from various and many directions as compared with the conventional polishing. Accordingly, first, biased wear of each abrasive grain is prevented. Next, on the upper surface of the polishing pad, it becomes easier to remove any clogging caused by fragments of the abrasive grains dropped off from the surface or fragments removed from the surface of the target substrate.
In a preferred embodiment of the polishing apparatus in accordance with the present invention, in the polishing apparatus described above, angular velocity of rotation of at least one of the surface plate axis and the substrate axis about the corresponding eccentric axis is made larger than that of the angular velocity of rotation of the target substrate about the substrate axis.
Accordingly, at least one of the polishing pad and the substrate to be polished revolves about the eccentric axis, at an angular velocity larger than the rotation about the substrate axis. Therefore, the slurry can be diffused uniformly with high efficiency between the polishing pad and the substrate to be polished.
In order to solve the above described technical problems, the present invention provides a polishing method in which slurry is supplied to an upper surface of a polishing pad rotated by a surface plate rotating shaft, a substrate to be polished is rotated by a substrate rotating shaft and the substrate to be polished is pressed against the polishing pad with a prescribed pressure, so that the surface of the target substrate is polished, including the step of rotating at least one of a surface plate axis as a rotation central axis of the surface plate rotating shaft and a substrate axis as a rotation central axis of the substrate rotating shaft, about a corresponding prescribed eccentric axis.
Accordingly, on the polishing pad, the distance of movement of the small area held by the substrate to be polished is increased and, hence, the contact area between the small area and the polishing pad can be increased.
Further, each abrasive grain held by the polishing pad comes to be brought into contact with a small area of the substrate to be polished from various and many directions as compared with the conventional polishing. Accordingly, first, bias wear of each abrasive grain can be prevented. Further, on the upper surface of the polishing pad, it becomes easier to remove any clogging generated by fragments of the abrasive grains dropped out from the surface or fragments removed from the surface of the target substrate.
In the preferred embodiment of the polishing method in accordance with the present invention, in the polishing method described above, at least one of the surface plate axis and the substrate axis is rotated about the corresponding prescribed eccentric axis at an angular velocity larger than that of rotation of the target substrate about the substrate axis.
Accordingly, at least one of the polishing pad and the substrate to be polished is revolved around the eccentric axis at an angular velocity larger than that of the rotation about the substrate axis. Therefore, it is possible to diffuse the slurry uniformly with high efficiency between the polishing pad and the substrate to be polished.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.